This invention relates to a novel process for the preparation of isocyanates containing silylated hydroxyl groups or silylated carboxyl groups as substituents and to the use of the compounds obtained by this process as reactants for isocyanatocarboxylic acid halides in the preparation of polyisocyanates containing ester groups.
The preparation of organic isocyanates containing silylated alcoholic hydroxyl groups as substituents is known. Silyloxyalkyl isocyanates, for example, are obtained by reaction of the amino alcohols corresponding to the isocyanates with bis(3-chlorophenyl)carbonate to produce N-(2-hydroxyalkyl)carbamic acid 4-chlorophenyl ester; silylation of the reaction product with trimethylchlorosilane in the presence of an equimolar quantity of triethylamine; and decomposition of the resulting carbamic acid ester. H. R. Kricheldorf, Liebigs Annalen der Chemie (1973), 772.
The preparation of aromatic isocyanates containing silylated phenolic hydroxyl groups as substituents by thermal decomposition of the corresponding O-phenylurethanes has also been described by H. R. Kricheldorf, see above reference. The ester used for this purpose must be prepared from N,O-bis-silylated aminophenols and chloroformic acid phenyl ester in the presence of triethylamine.
Another process for the preparation of isocyanates containing silylated hydroxyl groups is based on the reaction of trimethylsilyloxybenzoyl chloride with trimethylsilyl azide, the isocyanates being formed by Curtius degradation of the acid azides. The process is limited to trimethylsilyloxyaryl isocyanates because trimethylsilyloxyalkanoyl chlorides cannot be prepared, G. Schwarz, H. Alberts, H. R. Kricheldorf, Liebigs Annalen der Chemie (1981), 1257.
All of these processes known in the art are cumbersome multistage processes that are not generally applicable and that have hitherto been described only in the scientific literature, without significant practical technology having been demonstrated.
It has now surprisingly been found that organic isocyanates containing silylated hydroxyl groups or silylated carboxyl groups, preferably alcoholic or phenolic hydroxyl groups as substituents may easily be obtained by reaction at elevated temperatures of the corresponding O-silylated amino phenols, amino alcohols or aminocarboxylic acids with at least equivalent quantities of non-volatile organic polyisocyantes. The O-silylated starting materials used for this reaction may in turn be obtained by a simple reaction of the corresponding amino phenols, amino alcohols or aminocarboxylic acids with hexamethyldisilazane (HMDS).